In disc drive data storage devices a slider, including a recording head, flies over the disc and is separated from the disc by an air bearing. The rapid increase in the areal density of magnetic recording technology requires a significant decrease in the fly height (FH) of magnetic head sliders. As the FH decreases, an accurate control of FH under various environmental conditions such as temperature, altitude and humidity becomes even more important to ensure a reliable head-disc interface.
A known approach to FH control is to use an integrated heating element (called a “heater”) as an actuator for controlling the fly height in combination with a number of ways to measure the FH. As for the FH measurement, a Wallace equation-based harmonic ratio type approach (called ‘AR/HR’ method) has been used to provide a relative FH estimation together with a position error signal-based head-disc contact detection (called the “dPES” method) as a reference FH point.
Although dPES-based contact detection has been successfully implemented in disc drives, it would be desirable to provide an alternative contact detection scheme with improved results at small skew angles, and/or with reduced head-disc contact time.